1. Field
Aspects of the present invention relate to a method of separating a substrate and a method of fabricating a semiconductor device using the same, in which a sacrificial layer is patterned to form a void between a substrate and an epitaxial layer.
2. Discussion of the Background
A light emitting diode is an inorganic semiconductor device that emits light through the recombination of electrons and holes, and has recently been used in various fields, such as displays, vehicle lamps, lighting, and the like. Light emitting diodes may be classified into lateral light emitting diodes and vertical light emitting diodes according to the locations of electrodes.
Although the lateral light emitting diode is fabricated by a relatively simple method, the lateral light emitting diode has a problem in that a light emitting area is decreased, since a part of an active layer is removed for the formation of an electrode of a lower semiconductor layer. In addition, a p-type electrode and an n-type electrode of the lateral light emitting diode are arranged horizontally, thereby causing current crowding and lowering the luminous efficacy of the light emitting diode. Further, a sapphire substrate having low thermal conductivity is most widely used as a growth substrate of the lateral light emitting diode. However, the lateral light emitting diode having such a sapphire substrate has difficulty dissipating heat. Accordingly, junction temperature of light emitting diode is increased, thereby lowering internal quantum efficiency of the light emitting diode.
To solve the foregoing problems of lateral light emitting diodes, vertical light emitting diodes have been developed. In the vertical light emitting diode, electrodes are arranged in a vertical direction, and a growth substrate such as a sapphire substrate is separated from a semiconductor layer, thereby overcoming the foregoing problems of the lateral light emitting diode.
The vertical light emitting diode requires an additional process for separating the growth substrate, since the electrodes are arranged in the vertical direction. In general, a laser lift-off (LLO) process is used for separating the growth substrate. However, when the laser lift-off process is used to separate the growth substrate, the semiconductor layer can suffer from cracking due to the high energy of a laser beam. Further, when the growth substrate and the semiconductor layer are made of a homogeneous material (for example, a gallium nitride-based semiconductor layer and a gallium nitride substrate), it is difficult to apply the laser lift-off process due to small difference in energy band gap between the growth substrate and the semiconductor layer.
To solve such problems in the laser lift-off process of separating the growth substrate, a chemical lift-off (CLO) process, a stress lift-off (SLO) process, and the like, have been recently developed. In the chemical lift-off process, an etching solution infiltrates through a channel (in general, a void) formed between the semiconductor layer and the growth substrate such that the semiconductor layer and the growth substrate can be separated from each other. In the stress lift-off process, stress is applied after weakening coupling between the semiconductor layer and the growth substrate, such that the semiconductor layer and the growth substrate can be separated from each other.
To use the chemical lift-off process for separating the growth substrate, a method of forming a channel through which the etching solution can be infiltrated between the growth substrate and the semiconductor layer is used. For example, a sacrificial layer is formed between the semiconductor layer and the growth substrate, and a mask pattern is formed on the sacrificial layer. Then, the sacrificial layer is partially removed by electro-chemical etching (ECE), thereby forming a void in the sacrificial layer. Parts of the sacrificial layer arranged under a region not covered with the mask pattern are etched to form voids. The voids may be used as a transfer channel for the etching solution.
However, since the void has only a width of several micrometers, the etching solution supplied into the voids has a very slow etching rate. For example, in the chemical lift-off process, a buffered oxide etchant (BOE) employed as the etching solution is transferred at an etching rate of dozens of micrometers per hour, when the voids are used as the channel. Thus, it takes a long time to separate a 2 inch thickness substrate using the etching solution, and such void forming method is not suitable for separation of a large substrate.
Moreover, the method of forming voids using ECE has low reproducibility. As a result, the process of separating a substrate has low reproducibility and reliability, thereby lowering process yield.